The present application is directed to a system and method for accumulating hydraulic fluid. More particularly, the present invention is directed to a hydraulic system that uses an accumulator and control valves to store and regenerate energy.
Work machines are commonly used to move heavy loads, such as earth, construction material, and/or debris. These work machines, which may be, for example, wheel loaders, excavators, bull dozers, backhoes, telehandlers, and track loaders, typically include different types of work implements that are designed to perform various moving tasks. The work implements of these work machines are commonly powered by hydraulic systems, which use pressurized fluid to move the work implements.
A hydraulic system for an work machine typically includes a source of pressurized fluid, such as, for example, a pump, that is connected to a hydraulic actuator. A directional control valve is positioned between the source of pressurized fluid and the hydraulic actuator to control the flow of pressurized fluid into the actuator. When the control valve is opened, pressurized fluid is directed into one of two chambers in the hydraulic actuator. The fluid exerts a force on a moveable element in the hydraulic actuator, which causes the moveable element to move. The moveable element is, in turn, connected to the work implement. Movement of the moveable element translates to a corresponding movement in the work implement. When the moveable element moves, fluid is forced out of the second chamber of the hydraulic actuator.
Typically, the directional control valve directs the escaping fluid to a fluid reservoir tank or similar fluid receptacle.
In many situations, the work implement of the work machine is raised to an elevated position. As the work implement may be relatively heavy, the work implement gains significant potential energy when raised to the elevated position. When the work implement is released from the elevated position this potential energy is usually converted to heat when the pressurized fluid is throttled across a valve and returned to the tank. Some of the potential energy of a work implement in an elevated position may be captured by directing the pressurized fluid that escapes from the second chamber into an accumulator, which stores the fluid under pressure.
An exemplary hydraulic system on a work machine using a fluid accumulator for recovering or recycling load energy from a lifting cylinder is described in International Publication No. WO 00/00748 to Laars Bruun. As described therein however, an additional pump operated by the drive unit of the work machine is required to communicate fluid between the accumulator and the head end of the lifting cylinder. Depending upon the desired direction of movement of the lift cylinder, and the pressure difference between accumulator and cylinder, the drive unit supplies energy to, or receives energy from, the hydraulic circuit.
Another known use of an accumulator is to provide ride control. When an operator moves the earth moving machine over an uneven surface, such as when carrying a load around a job site, the work implement tends to bounce and jar if held rigidly by the hydraulic system. The bouncing of the work implement may be decreased by connecting the accumulator to the load bearing chamber of the hydraulic actuator. The pressurized fluid stored in the accumulator acts as a shock absorber and reduces the bouncing of the work implement. In this manner, a smoother ride for the earth moving machine may be achieved. The energy required to charge the accumulator to the same pressure as the cylinder prior to initiating ride control is commonly provided entirely by the pump however, and no provision is made for making use of that stored energy when ride control is terminated.
The hydraulic system of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a hydraulic system that includes a hydraulic actuator, a source of pressurized fluid, and a directional control valve controlling fluid flow into and out of the hydraulic actuator. An accumulator is disposed between a fluid input line and a fluid output line for the directional control valve. A regeneration control valve is disposed between the accumulator and the output of the source of pressurized fluid. A storage control valve is disposed between the fluid output line and a tank of the hydraulic system.
In another aspect, the present invention is directed to a method of regenerating energy in a hydraulic system. Pressurized fluid is from one of a plurality of hydraulic actuators using a directional control valve. At least a portion of the fluid released from the hydraulic actuator is stored under pressure in an accumulator disposed between a fluid input line and a fluid output line of the directional control valve. Energy stored in the accumulator is regenerated by releasing the fluid stored under pressure to operate a hydraulic actuator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.